IN-VITRO MATURATION OF HUMAN GERMINAL VESICLE STAGE OOCYTES - ROLE OFCUMULUS CELLS AND EPIDERMAL GROWTH-FACTOR IN THE CULTURE-MEDIUM

In-vitro maturation (IVM) of oocytes is a promising technique to reduc e the costs and avert the side-effects of gonadotrophin stimulation fo r in-vitro fertilization (IVF). The pregnancy rates from oocytes matur ed in vitro are much lower than those of in-vivo stimulation cycles in dicating that optimization of IVM remains a challenge. Therefore, we i nvestigated the effect of supplementation of the medium with gonadotro phins, oestradiol and epidermal growth factor (EGF) and the effect of retaining or removing the cumulus cells on nuclear and cytoplasmic mat uration of immature oocytes. Human germinal vesicle (GV) oocytes obtai ned after gonadotrophin stimulation for intracytoplasmic sperm injecti on (ICSI) were cultured in a complex defined medium either supplemente d with gonadotrophins, oestradiol and physiological concentrations of EGF (2 ng/ml) or gonadotrophins and oestradiol alone. The cumulus cell s were either removed or kept intact. In GV stage oocytes cultured wit hout cumulus (group I) significantly more oocytes reached the metaphas e II (MII) stage at 30 h in media supplemented with EGF (64.3 versus 3 3.9%, P < 0.003). For oocytes cultured with intact cumulus (group II), more oocytes reached MII at 30 h than in group I, but there was no di fference in medium with or without EGF supplementation (81.8 and 79.8% respectively). Cytoplasmic maturation of MII oocytes was judged from their capability to activate and fertilize after ICSI, In group I, the rates of activation and normal fertilization were similar, However, i n group II, significantly more oocytes underwent normal fertilization in the EGF-supplemented than the unsupplemented group (71.7 versus 45. 6%, P < 0.05). The cleavage rates of the fertilized oocytes were simil ar in the sibling oocyte subgroups cultured with or without EGF supple mentation, but the overall cleavage rates were higher in cumulus-intac t compared to cumulus-denuded oocytes (88.9 versus 47.8%, P < 0.001). Thus, supplementation of the maturation medium with EGF and maintenanc e of the cumulus during culture improve the nuclear and cytoplasmic ma turation of human oocytes in vitro.